1. Field of the Invention
The present invention relates to an active vibratory noise control apparatus for actively controlling vibratory noise using adaptive notch filters, the active vibratory noise control apparatus being adapted for use in motor vehicles.
2. Description of the Related Art
Heretofore, it has been general practice in the field of active vibratory noise control in vehicle passenger compartments to model signal transfer characteristics to be controlled with a FIR filter, supply the FIR filter with input pulses based on the engine rotational speed and suspension vibration outputs that are highly correlated to vibratory noise to be controlled, use an output signal from the FIR filter as a reference signal, adaptively generate a signal to produce canceling vibratory noise for reducing an error signal from the reference signal and the error signal, and apply the generated signal to an actuator to produce secondary vibratory noise to reduce the vibratory noise.
According to an example of the above active vibratory noise control process, a reference wave signal is generated by a reference wave signal generator in response to an engine rotational speed signal, the generated reference wave signal is applied to an adaptive FIR filter, which produces an output signal to drive a speaker. The difference between vibratory noise caused in a vehicle passenger compartment by the output energy radiated from the speaker and vibratory noise produced in the vehicle passenger compartment by engine rotation, etc. is detected by a microphone installed in the vehicle passenger compartment, and the adaptive FIR filter is controlled to reduce an output signal from the microphone (see, for example, Japanese Laid-Open Patent Publication No. 1-501344 (PCT application)).
Another example is known as an active vibratory noise control apparatus employing adaptive notch filters, as shown in FIG. 17 of the accompanying drawings. This active vibratory noise control apparatus is based on the fact that vibratory noise in a vehicle passenger compartment is generated in synchronism with the rotation of the output shaft of the engine. The vibratory noise that is produced in the vehicle passenger compartment at a frequency based on the rotation of the output shaft of the engine is silenced using the adaptive notch filters.
In the known active vibratory noise control apparatus employing adaptive notch filters, as shown in FIG. 17, engine pulses which are synchronous with the rotation of the output shaft of the engine are shaped in waveform by a waveform shaper 71, whose output signal is applied to a cosine wave generator 72 and a sine wave generator 73 which generate a cosine wave signal and a sine wave signal, respectively. The cosine wave signal is passed through an adaptive notch filter 74, and the sine wave signal is passed through an adaptive notch filter 75. Output signals from the adaptive notch filters 74, 75 are added by an adder 76 into a sum signal, which is applied to energize a secondary vibratory noise generator 77.
The cosine wave signal is applied to a transfer element 78 having passenger-compartment signal transfer characteristics (γ0) for the frequency in synchronism with the rotation of the engine output shaft, and the sine wave signal is applied to a transfer element 79 having passenger-compartment signal transfer characteristics (γ1) for the frequency in synchronism with the rotation of the engine output shaft. Output signals from the transfer elements 78, 79 are added into a first reference signal by an adder 80. The sine wave signal is applied to a transfer element 81 having the passenger-compartment signal transfer characteristics (γ0), and the cosine wave signal is applied to a transfer element 82 having passenger-compartment signal transfer characteristics (−γ1). Output signals from the transfer elements 81, 82 are added into a second reference signal by an adder 83. The filter coefficients of the adaptive notch filter 74 are updated according to an adaptive algorithm based on the first reference signal, and the filter coefficients of the adaptive notch filter 75 are updated according to an adaptive algorithm based on the second reference signal, so that an error signal detected by an error detecting means 86 will be minimized. For details, reference should be made to Japanese Laid-Open Patent Publication No. 2000-99037, for example.
The above example of the active vibratory noise control process which employs an FIR filter for producing a reference signal (for example, Japanese Laid-Open Patent Publication No. 1-501344 (PCT application)) is problematic in that because of convolutional calculations to be done by the FIR filter, if the active vibratory noise control process is to cancel passenger-compartment vibratory noise at rapid accelerations of the vehicle, the sampling frequency needs to be increased, and the number of taps of the FIR filter also needs to be increased, with the results that the processing load on the FIR filter is large, and an active vibratory noise control apparatus for performing the active vibratory noise control process requires a processor having a large processing capability, such as a digital signal processor, and hence is highly expensive.
The active vibratory noise control apparatus employing adaptive notch filters (for example, Japanese Laid-Open Patent Publication No. 2000-99037) is disadvantageous in that though the amount of calculations required to produce reference signals may be small, the signal transfer characteristics from the secondary vibratory noise generator to the error signal detecting means is not sufficiently optimally modeled, and optimum reference signals for updating the filter coefficients of the adaptive notch filters are not obtained, with the results that the active vibratory noise control apparatus may find it difficult to cancel passenger-compartment vibratory noise at rapid accelerations of the vehicle and fail to provide a sufficient vibratory noise control capability.
The applicant of the present application has proposed an active vibratory noise control apparatus having a storage device having a memory for storing a cosine corrective value, in association with a control frequency, based on the cosine value of a phase lag in the signal transfer characteristics between a speaker and a microphone, and a memory for storing a sine corrective value, in association with the control frequency, based on the sine value of the phase lag in the signal transfer characteristics between the speaker and the microphone. The cosine corrective value read from the storage device and a reference cosine signal output from a cosine wave generating circuit are multiplied by each other, and the sine corrective value read from the storage device and a reference sine signal output from a sine wave generating circuit are multiplied by each other. The product signals are processed into a first reference signal. The cosine corrective value read from the storage device and the reference sine signal output from the sine wave generating circuit are multiplied by each other, and the sine corrective value read from the storage device and the reference cosine signal output from a cosine wave generating circuit are multiplied by each other. The product signals are processed into a second reference signal. For details, reference should be made to Japanese Laid-Open Patent Publication No. 2004-361721. The applicant of the present application is one of the co-applicants of Japanese Laid-Open Patent Publication No. 2004-361721.